Infiltrated NiCo Alloy Nanoparticle Decorated Perovskite Oxide: A Highly Active,Stable, and Antisintering Anode for Direct‐Ammonia Solid Oxide Fuel Cells

Direct ammonia solid oxide fuel cell (DA‐SOFC) is superior to low‐temperature direct ammonia fuel cell using anion exchange membrane because of much improved anode reaction kinetics at elevated temperature. However, significant performance degradation due to severe sintering of conventional nickel cermet anode under operating conditions is a big challenge for realizing its practical use. Herein, a high‐performance anode based on La_0.55Sr_0.30TiO_3?δ (LST) perovskite substrate with its surface decorated with in situ exsolved and strongly coupled NiCo alloy nanoparticles (NPs) is designed and fabricated for DA‐SOFCs, exhibiting superior catalytic activity for NH₃ decomposition reaction due to balanced NH₃ adsorption and N₂ desorption processes. An electrolyte‐supported single cell with infiltrated NiCo/LST on Sm_0.2Ce_0.8O_1.9 scaffold anode delivers a maximum power density of 361 mW cm^?2 at 800 °C in NH₃ fuel, superior to similar SOFCs with Ni or Co NP‐decorated LST based anodes (161 and 98 mW cm^?2). Furthermore, the SOFC with this newly developed anode displays favorable operational stability without obvious performance degradation at 700 °C for a test period of ≈120 h, attributed to its high antisintering capability. This study provides some strategies to develop highly active, stable, and antisintering perovskite‐based nanocomposite for DA‐SOFCs, facilitating the practical use of this technology.     

Catalytic properties of Pt cluster-decorated CeO2 nanostructures

Uniform clusters of Pt have been deposited on the surface of capping-agent-free CeO₂ nanooctahedra and nanorods using electron beam (e-beam) evaporation. The coverage of the Pt nanocluster layer can be controlled by adjusting the e-beam evaporation time. The resulting e-beam evaporated Pt nanocluster layers on the CeO₂ surfaces have a clean surface and clean interface between Pt and CeO₂. Different growth behaviors of Pt on the two types of CeO₂ nanocrystals were observed, with epitaxial growth of Pt on CeO₂ nanooctahedra and random growth of Pt on CeO₂ nanorods. The structures of the Pt clusters on the two different types of CeO₂ nanocrystals have been studied and compared by using them as catalysts for model reactions. The results of hydrogenation reactions clearly showed the clean and similar chemical surface of the Pt clusters in both catalysts. The support-dependent activity of these catalysts was demonstrated by CO oxidation. The Pt/CeO₂ nanorods showed much higher activity compared with Pt/CeO₂ nanooctahedra because of the higher concentration of oxygen vacancies in the CeO₂ nanorods. The structure-dependent selectivity of dehydrogenation reactions indicates that the structures of the Pt on CeO₂ nanorods and nanooctahedra are different. Thes differences arise because the metal deposition behaviors are modulated by the strong metal-metal oxide interactions.     

Anodes for Direct Oxidation of Dry Hydrocarbons in a Solid‐Oxide Fuel Cell

The manufacture of fuel cells that can operate directly on various hydrocarbon fuels, without the need for reforming, has the potential of greatly speeding the application of fuel cells for transportation and distributed‐power applications. This paper will briefly review the literature in this area and describe recent developments in solid‐oxide fuel cells (SOFCs) that demonstrate that direct‐oxidation fuel cells are possible with Cu‐based anodes. A new method for synthesizing thin‐electrolyte, anode‐supported cells is described that is based on tape casting with graphite pore formers (see Figure), followed by impregnation with aqueous solutions of Cu(NO₃)₂ and Ce(NO₃)₃. The performance of model SOFCs for direct conversion of n‐butane and methane is shown. Finally, future developments that are needed for this technology to be commercialized are discussed.     

FeS2 Nanoparticles Decorated Graphene as Microbial‐Fuel‐Cell Anode Achieving High Power Density

Microbial fuel cells (MFCs) have received great attention worldwide due to their potential in recovering electrical energy from waste and inexhaustible biomass. Unfortunately, the difficulty of achieving the high power, especially in real samples, remains a bottleneck for their practical applications. Herein, FeS₂ nanoparticles decorated graphene is fabricated via a simple hydrothermal reaction. The FeS₂ nanoparticles decorated graphene anode not only benefits bacterial adhesion and enrichment of electrochemically active Geobacter species on the electrode surface but also promotes efficient extracellular electron transfer, thus giving rise to a fast start‐up time of 2 d, an unprecedented power density of 3220 mW m^?2 and a remarkable current density of 3.06 A m^?2 in the acetate‐feeding and mixed bacteria‐based MFCs. Most importantly, the FeS₂ nanoparticles decorated graphene anode successfully achieves a power density of 310 mW m^?2 with simultaneous removal of 1319 ± 28 mg L^?1 chemical oxygen demand in effluents from a beer factory wastewater. The characteristics of improved power generation and enhanced pollutant removal efficiency opens the door toward development of high‐performance MFCs via rational anode design for practical application.     

Iron‐Free Cathode Catalysts for Proton‐Exchange‐Membrane Fuel Cells: Cobalt Catalysts and the Peroxide Mitigation Approach

High‐performance and inexpensive platinum‐group‐metal (PGM)‐free catalysts for the oxygen reduction reaction (ORR) in challenging acidic media are crucial for proton‐exchange‐membrane fuel cells (PEMFCs). Catalysts based on Fe and N codoped carbon (Fe–N–C) have demonstrated promising activity and stability. However, a serious concern is the Fenton reactions between Fe²⁺ and H₂O₂ generating active free radicals, which likely cause degradation of the catalysts, organic ionomers within electrodes, and polymer membranes used in PEMFCs. Alternatively, Co–N–C catalysts with mitigated Fenton reactions have been explored as a promising replacement for Fe and PGM catalysts. Therefore, herein, the focus is on Co–N–C catalysts for the ORR relevant to PEMFC applications. Catalyst synthesis, structure/morphology, activity and stability improvement, and reaction mechanisms are discussed in detail. Combining experimental and theoretical understanding, the aim is to elucidate the structure–property correlations and provide guidance for rational design of advanced Co catalysts with a special emphasis on atomically dispersed single‐metal‐site catalysts. In the meantime, to reduce H₂O₂ generation during the ORR on the Co catalysts, potential strategies are outlined to minimize the detrimental effect on fuel cell durability.     

Stable High‐Index Faceted Pt Skin on Zigzag‐Like PtFe Nanowires Enhances Oxygen Reduction Catalysis

Selectively exposing active surfaces and judiciously tuning the near‐surface composition of electrode materials represent two prominent means of promoting electrocatalytic performance. Here, a new class of Pt₃Fe zigzag‐like nanowires (Pt‐skin Pt₃Fe z‐NWs) with stable high‐index facets (HIFs) and nanosegregated Pt‐skin structure is reported, which are capable of substantially boosting electrocatalysis in fuel cells. These unique structural features endow the Pt‐skin Pt₃Fe z‐NWs with a mass activity of 2.11 A mg^?1 and a specifc activity of 4.34 mA cm^?2 for the oxygen reduction reaction (ORR) at 0.9 V versus reversible hydrogen electrode, which are the highest in all reported PtFe‐based ORR catalysts. Density function theory calculations reveal a combination of exposed HIFs and formation of Pt‐skin structure, leading to an optimal oxygen adsorption energy due to the ligand and strain effects, which is responsible for the much enhanced ORR activities. In contrast to previously reported HIFs‐based catalysts, the Pt‐skin Pt₃Fe z‐NWs maintain ultrahigh durability with little activity decay and negligible structure transformation after 50 000 potential cycles. Overcoming a key technical barrier in electrocatalysis, this work successfully extends the nanosegregated Pt‐skin structure to nanocatalysts with HIFs, heralding the exciting prospects of high‐effcient Pt‐based catalysts in fuel cells.     

Cell-protecting regeneration from anode carbon deposition using in situ produced oxygen and steam: A combined experimental and theoretical study

Carbon deposition is a primary concern during the operation of solid oxide fuel cells (SOFCs) fueled with hydrocarbon fuels, leading to cell degradation and even cell damage. Carbon elimination is expected to be a promising approach to prolong cell life. This work reports on a combined experimental and theoretical investigation of cell regeneration from anode carbon deposition of tubular SOFCs fabricated by phase-inversion and co-sintering techniques. The as-prepared cell exhibits a maximum power density of 0.20?W?cm^?2 at 800?°C fueling with wet CH₄, but fails to stable operation due to severe carbon deposition. Based on thermodynamic predictions, a successive cell-protecting regeneration process is proposed to eliminate deposited carbon without oxidizing Ni catalysts, during which CH₄ and H₂ fuels are provided in circulation. Through a total of 35 cycling tests, cell performance can always successfully restore to the initial level. The possible carbon elimination mechanism is investigated in detail based on thermodynamic and first-principle calculations. The feasibility of carbon elimination using in situ produced oxygen or steam through electrochemical reaction has been revealed, providing a novel continuous operation mode for hydrocarbon-based SOFCs.     

Skin‐Like Stretchable Fuel Cell Based on Gold‐Nanowire‐Impregnated Porous Polymer Scaffolds

Skin‐like energy devices can be conformally attached to the human body, which are highly desirable to power soft wearable electronics in the future. Here, a skin‐like stretchable fuel cell based on ultrathin gold nanowires (AuNWs) and polymerized high internal phase emulsions (polyHIPEs) scaffolds is demonstrated. The polyHIPEs can offer a high porosity of 80% yet with an overall thickness comparable to human skin. Upon impregnation with electronic inks containing ultrathin (2 nm in diameter) and ultrahigh aspect‐ratio (>10 000) gold nanowires, skin‐like strain‐insensitive stretchable electrodes are successfully fabricated. With such designed strain‐insensitive electrodes, a stretchable fuel cell is fabricated by using AuNWs@polyHIPEs, platinum (Pt)‐modified AuNWs@polyHIPEs, and ethanol as the anode, cathode, and fuel, respectively. The resulting epidermal fuel cell can be patterned and transferred onto skin as “tattoos” yet can offer a high power density of 280 µW cm^?2 and a high durability (>90% performance retention under stretching, compression, and twisting). The results presented here demonstrate that this skin‐thin, porous, yet stretchable electrode is essentially multifunctional, simultaneously serving as a current collector, an electrocatalyst, and a fuel host, indicating potential applications to power future soft wearable 2.0 electronics for remote healthcare and soft robotics.     

Nanostructured Metal‐Free Electrochemical Catalysts for Highly Efficient Oxygen Reduction

Replacing precious and nondurable Pt catalysts with cheap and commercially available materials to facilitate sluggish cathodic oxygen reduction reaction (ORR) is a key issue in the development of fuel cell technology. The recently developed cost effective and highly stable metal‐free catalysts reveal comparable catalytic activity and significantly better fuel tolerance than that of current Pt‐based catalysts; therefore, they can serve as feasible Pt alternatives for the next generation of ORR electrocatalysts. Their promising electrocatalytic properties and acceptable costs greatly promote the R&D of fuel cell technology. This review provides an overview of recent advances in state‐of‐the‐art nanostructured metal‐free electrocatalysts including nitrogen‐doped carbons, graphitic‐carbon nitride (g‐C₃N₄)‐based hybrids, and 2D graphene‐based materials. A special emphasis is placed on the molecular design of these electrocatalysts, origin of their electrochemical reactivity, and ORR pathways. Finally, some perspectives are highlighted on the development of more efficient ORR electrocatalysts featuring high stability, low cost, and enhanced performance, which are the key factors to accelerate the commercialization of fuel cell technology.     

Disordering and the electronic transport behaviors of NbC–Al<Subscript>4</Subscript>C<Subscript>3</Subscript>–C composite

A composite nanomaterial composed of NbC nanocrystals, Al₄C₃ nanorods and carbon nanofibers as well as amorphous carbon was fabricated by arc-discharging a Nb₃Al block as an anode in CH₄ gas. The growth process of the NbC–Al₄C₃–C composite was deduced according to the microstructures of its components and the experimental conditions. NbC nanocrystals with non-stoichiometric chemical composition were in a cubic shape. As the decomposition product of the precursor of CH₄ gas, carbon nanofibers were thought to be as templates, reacting with Al atoms, to form Al₄C₃ nanorods with a diameter of 15–40 nm. A thin layer of aluminum carbide oxide covered the surface of Al₄C₃ nanorods. The temperature dependence of the resistivity for the NbC–Al₄C₃–C composite was described by the variable-range-hopping (VRH) model between about 100 K and 300 K because of the strong localization of electrons by disorder in the carbon matrix. Below 100 K, the transport behaviors of the pellet deviated from the VRH model due to the conduction competition between the semi-conducting carbon matrix and metallic NbC nanocrystals.     

Shape and composition-controlled platinum alloy nanocrystals using carbon monoxide as reducing agent

The shape of metal alloy nanocrystals plays an important role in catalytic performances. Many methods developed so far in controlling the morphologies of nanocrystals are however limited by the synthesis that is often material and shape specific. Here we show using a gas reducing agent in liquid solution (GRAILS) method, different Pt alloy (Pt-M, M = Co, Fe, Ni, Pd) nanocrystals with cubic and octahedral morphologies can be prepared under the same kind of reducing reaction condition. A broad range of compositions can also be obtained for these Pt alloy nanocrystals. Thus, this GRAILS method is a general approach to the preparation of uniform shape and composition-controlled Pt alloy nanocrystals. The area-specific oxygen reduction reaction (ORR) activities of Pt(3)Ni catalysts at 0.9 V are 0.85 mA/cm(2)(Pt) for the nanocubes, and 1.26 mA/cm(2)(Pt) for the nanooctahedra. The ORR mass activity of the octahedral Pt(3)Ni catalyst reaches 0.44 A/mg(Pt).     

Energy Transfer in Ionic‐Liquid‐Functionalized Inorganic Nanorods for Highly Efficient Photocatalytic Applications

Energy transfer in self‐assembled ionic liquids (ILs) and iron oxyhydroxide nanocrystals and the controlled surface chemistry of functionalized nanomaterials for photocatalytic applications are reported. Self‐assembled ILs play the role of multifunctional materials in terms of constructing a well‐designed nanostructure, controlling the surface chemistry, and triggering the energy transfer of functionalized materials. IL‐functionalized β‐FeOOH nanorods show ≈10‐fold higher performances than those of commercial materials due to the synergistic effect of well‐defined nanomaterials in diffusion‐controlled reactions, specific interactions with target pollutants, and energy transfers in hybrid materials. In particular, the energy transfer in C₄MimCl‐functionalized β‐FeOOH nanorods enhances photocatalytic activity due to the generation of Fe²⁺. The strategy described herein provides new insight into the rational design of functionalized inorganic nanomaterials for applications in emerging technologies.     

High-Performance Ammonia Protonic Ceramic Fuel Cells Using a Pd Inter-Catalyst

This study reports the performance and durability of a protonic ceramic fuel cells (PCFCs) in an ammonia fuel injection environment. The low ammonia decomposition rate in PCFCs with lower operating temperatures is improved relative to that of solid oxide fuel cells by treatment with a catalyst. By treating the anode of the PCFCs with a palladium (Pd) catalyst at 500 °C under ammonia fuel injection, the performance (peak power density of 340 mW cm⁻² at 500 °C) is approximately two-fold higher than that of the bare sample not treated with Pd. Pd catalysts are deposited through an atomic layer deposition post-treatment process on the anode surface, in which nickel oxide (NiO) and BaZr_0.2Ce_0.6Y_0.1Yb_0.1O_3–δ (BZCYYb) are mixed, and Pd can penetrate the anode surface and porous interior. Impedance analysis confirmed that Pd increased the current collection and significantly reduced the polarization resistance, particularly in the low-temperature region (≈500 °C), thereby improving the performance. Furthermore, stability tests showed that superior durability is achieved compared with that of the bare sample. Based on these results, the method presented herein is expected to represent a promising solution for securing high-performance and stable PCFCs based on ammonia injection.     

WO3-Assisted Synergetic Effect Catalyzes Efficient and CO-Tolerant Hydrogen Oxidation for PEMFCs

Developing anode catalysts with substantially enhanced activity for hydrogen oxidation reaction (HOR) and CO tolerance performance is of great importance for the commercial applications of proton exchange membrane fuel cells (PEMFCs). Herein, an excellent CO-tolerant catalyst (Pd-WO₃/C) has been fabricated by loading Pd nanoparticles on WO₃ via an immersion-reduction route. A remarkably high power density of 1.33 W cm⁻² at 80 °C is obtained by using the optimized 3Pd-WO₃/C as the anode catalyst of PEMFCs, and the moderately reduced power density (73% remained) in CO/H₂ mixed gas can quickly recover after removal of CO-contamination from hydrogen fuel, which is not possible by using Pt/C or Pd/C as anode catalyst. The prominent HOR activity of 3Pd-WO₃/C is attributed to the optimized interfacial electron interaction, in which the activated H* adsorbed on Pd species can be effectively transferred to WO₃ species through hydrogen spillover effect and then oxidized through the H species insert/output effect during the formation of H_xWO₃ in acid electrolyte. More importantly, a novel synergetic catalytic mechanism about excellent CO tolerance is proposed, in which Pd and WO₃ respectively absorbs/activates CO and H₂O, thus achieving the CO electrooxidation and re-exposure of Pd active sites for CO-tolerant HOR.     

Characterization of electrolyte films deposited by using RF magnetron sputtering a 20 mol% gadolinia-doped ceria target

20 mol% Gd-doped ceria (20GDC) electrolyte films on poly-crystalline Al₂O₃ substrates were prepared by radio frequency (RF) magnetron sputtering from a 20GDC oxide target, which was made by the processes of colloidal dispersion-pressure casting-sintering. Material characteristics of the 20GDC oxide target and the deposited films before and after annealed at 900 °C for 2 h were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and conductivity measurements. Crack-free and dense 20GDC electrolyte films were observed by the deposition conditions of 200 W (RF power). Homogeneity tests revealed the chemical compositions (Ce and Gd) were uniformly distributed through the bulk of the target and the deposited films. 20GDC film with a comparable conductivity of 1.00 × 10^− 3 S/cm at 650 °C is higher than that of bulk yttria-stabilized zirconia (YSZ), but smaller than that of bulk GDCs (10GDC and 20 GDC). Sputtered-GDC films in this study can be also suggested to be used as the electrolyte films for solid oxide fuel cells (SOFCs) systems as compared to the well-known YSZ.     

Uniform Ag Nanocubes Prepared by AgCl Particle–Mediated Heterogeneous Nucleation and Disassembly and Their Mechanism Study by DFT Calculation

Uniform Ag nanocubes are reproducibly synthesized by a AgCl particle‐mediated heterogeneous nucleation and disassembly process in polyol chemistry. By introducing N,N‐dimethylformamide (DMF) in a conventional polyol method with HCl etchant, Ag nanocrystals (NCs) begin to be nucleated on the surface of AgCl‐precipitated particles due to the promoted reduction reaction by DMF. The nucleated Ag NCs on the AgCl particles are grown to Ag nanocubes in shape by consuming Ag sources from the AgCl mother particles. Eventually the grown Ag nanocubes are disassembled from the mother AgCl particles because the AgCl particles are fully digested by the growing Ag nanocubes. Density functional theory calculation confirms that the Ag atoms can be favorably deposited on the (100) facet of AgCl particles and the Ag nuclei on the AgCl particles tend to reveal (100) facet.     

One‐Pot Hydrothermal Synthesis of FeMoO4 Nanocubes as an Anode Material for Lithium‐Ion Batteries with Excellent Electrochemical Performance

Metal molybdates nanostructures hold great promise as high‐performance electrode materials for next‐generation lithium‐ion batteries. In this work, the facial design and synthesis of monodisperse FeMoO₄ nanocubes with the edge lengths of about 100 nm have been successfully prepared and present as a novel anode material for highly efficient and reversible lithium storage. Well‐defined single‐crystalline FeMoO₄ with high uniformity are first obtained as nanosheets and then self‐aggregated into nanocubes. The morphology of the product is largely controlled by the experimental parameters, such as the reaction temperature and time, the ratio of reactant, the solution viscosity, etc. The molybdate nanostructure would effectively promote the insertion of lithium ions and withstand volume variation upon prolonged charge/discharge cycling. As a result, the FeMoO₄ nanocubes exhibit high reversible capacities of 926 mAh g⁻¹ after 80 cycles at a current density of 100 mA g⁻¹ and remarkable rate performance, which indicate that the FeMoO₄ nanocubes are promising materials for high‐power lithium‐ion battery applications.     

Worm‐Shape Pt Nanocrystals Grown on Nitrogen‐Doped Low‐Defect Graphene Sheets: Highly Efficient Electrocatalysts for Methanol Oxidation Reaction

Although direct methanol fuel cell offers high energy use efficiency and low pollution emission, the lack of suitable electrode materials poses a great challenge to its commercial application. Herein, a facile and scalable approach is developed to fabricate a hybrid electrocatalyst consisting of strongly coupled worm‐shape Pt nanocrystals and nitrogen‐doped low‐defect graphene (N‐LDG) sheets. Interestingly, it is found that the formation of Pt nanoworms (NWs) is induced by the N atoms in the high‐quality carbon matrix, which also allows the integration of their respective structural advantages and leads to a strong synergetic coupling effect. As a result, the obtained Pt NW/N‐LDG catalyst exhibits an extremely high mass activity of 1283.1 mA mg^?1 toward methanol oxidation reaction, accompanied by reliable long‐term stability and good antipoisoning ability, which are dramatically enhanced as compared with conventional Pt nanoparticle catalysts dispersed on undoped LDG, reduced graphene oxide, and commercial carbon black supports.     

Ultrathin PtPd‐Based Nanorings with Abundant Step Atoms Enhance Oxygen Catalysis

The lack of highly active and stable catalysts with low Pt usage for the oxygen reduction reaction (ORR) is a major barrier in realizing fuel cell‐driven transportation applications. A general colloidal chemistry method is demonstrated for making a series of ultrathin PtPdM (M = Co, Ni, Fe) nanorings (NRs) for greatly boosting ORR catalysis. Different from the traditional ultrathin nanosheets, the ultrathin PtPdM NRs herein have a high portion of step atoms on the edge, high Pt utilization efficiency, and strong ligand effect from M to Pt and fast mass transport of reactants to the NRs. These key features make them exhibit greatly enhanced electrocatalytic activity for the ORR and the oxygen evolution reaction (OER). Among all the PtPdM NRs, the PtPdCo shows the highest ORR mass and specific activities of 3.58 A mg^?1 and 4.90 mA cm^?2 at 0.9 V versus reversible hydrogen electrode (RHE), 23.9 and 24.5‐fold larger than those of commercial Pt/C in alkaline electrolyte, respectively. The theoretical calculations reveal that the oxygen adsorption energy (E _O) can be optimized under the presence of step atoms exposed on the edge and ligand effect induced by Co. They are stable under ORR conditions with negligible changes after 30 000 cycles.     

Alumina‐Supported CoFe Alloy Catalysts Derived from Layered‐Double‐Hydroxide Nanosheets for Efficient Photothermal CO2 Hydrogenation to Hydrocarbons

A series of novel CoFe‐based catalysts are successfully fabricated by hydrogen reduction of CoFeAl layered‐double‐hydroxide (LDH) nanosheets at 300–700 °C. The chemical composition and morphology of the reaction products (denoted herein as CoFe‐x) are highly dependent on the reduction temperature (x). CO₂ hydrogenation experiments are conducted on the CoFe‐x catalysts under UV–vis excitation. With increasing LDH‐nanosheet reduction temperature, the CoFe‐x catalysts show a progressive selectivity shift from CO to CH₄, and eventually to high‐value hydrocarbons (C₂₊). CoFe‐650 shows remarkable selectivity toward hydrocarbons (60% CH₄, 35% C₂₊). X‐ray absorption fine structure, high‐resolution transmission electron microscopy, Mössbauer spectroscopy, and density functional theory calculations demonstrate that alumina‐supported CoFe‐alloy nanoparticles are responsible for the high selectivity of CoFe‐650 for C₂₊ hydrocarbons, also allowing exploitation of photothermal effects. This study demonstrates a vibrant new catalyst platform for harnessing clean, abundant solar‐energy to produce valuable chemicals and fuels from CO₂.